Sewage systems are in wide spread use for the removal of liquid waste from houses, factories and agricultural sites. The sewage flows through pipes into intermediate wells and finally into treatment plants or waste dumps. Electric pumps are usually used to maintain the flow and keep the wells below maximum capacity. These pumps are configured to operate when the level in the wells reaches a preset limit indicating that the flow needs pumping.
When the well level falls to a minimum level the pump is switched off and this level may be maintained for some time leaving a biofilm residue on the walls of the well between the maximum and minimum levels. This residue tends to harden and build up thus reducing the capacity of the well, and increasing the frequency of the pump operation.
Wastewater collection and treatment systems are a source of bad odors, the most prevalent coming from Hydrogen Sulphide, a toxic and corrosive gas with a characteristic rotten-egg smell. This is a bacterially mediated process that occurs in the submerged portion of sanitary sewerage systems. It begins with the establishment of a slime layer below the water level, composed of bacteria and other inert solids held together by a biologically secreted protein “glue” or biofilm called zooglea. When this biofilm becomes thick enough to prevent the diffusion of dissolved oxygen, an anoxic zone develops under the surface.
Hydrogen Sulphide is also a precursor to the formation of Sulphuric Acid, which causes the destruction of metal and concrete substrates and appurtenances within wastewater facilities and collection stations. The effect of biogenic sulfide corrosion and the formation of a 7% Sulphuric Acid solution on concrete surfaces exposed to the sewer environment are devastating. Entire pump stations and manholes and large sections of collection interceptors have collapsed due to the loss of structural integrity in the concrete.
Accordingly the residue must be cleaned off the well walls and removed from the surface of the sewer water periodically to maintain the system in good working order as well as protecting concrete structures against the biogenic sulfide corrosion in wastewater collection and treatment systems so as to met the structure's anticipated design life as well as protecting the surrounding ground level infrastructure and environment.
Manual cleaning of wells is time consuming, expensive and dirty work and a number of devices have been developed to automate and reduce the cost of cleaning. For example U.S. Pat. No. 4,431,232 teaches apparatus with a spray head comprising spray arms which are rotated about a vertical axis by a shaft driven by a motor and are rotated about a horizontal axis. As well as the complex gearing for the spray head the apparatus also requires a feed stream of pre-heated water and a chemical cleansing liquid. As the apparatus has still to be manually operated in the well it is a costly solution to the problem of cleaning sewage wells.
Another apparatus is disclosed in WO 01/58605 which is permanently mounted in the well on a support arm and connected to a cleaning liquid supply which is turned on and off by liquid control valves operated by level sensors in the well. However this apparatus still requires a separate cleaning liquid supply and uses a large volume of water which must be supplied from often scarce potable water sources.
U.S. Pat. No. 6,868,857 teaches a precursor apparatus to the present invention which is also permanently mounted in the well. It has a number of modifications aimed at making the wall cleaning action more effective and also has a deodorizing function. However the apparatus is still not completely effective and periodic manual cleaning of the well walls and maintenance of the apparatus requires time consuming dismantling and reassembly. The apparatus also still requires a large volume of water from an external supply of often scarce potable water.
It will be noted that U.S. Pat. No. 6,868,857 also teaches the use of the sewage in the well to feed the cleaning apparatus. However the latter system employs filters to remove solids from the sewage which is drawn into the submersible pump for pumping into the feed steam. But these filters quickly become clogged and the pump becomes ineffective and the apparatus reverts to using the external water supply. Further this method of using filtered effluent is not effective in chopping up and removing the biofilm construction.